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CVE-2026-21870— The BACnet Protocol Stack library has an Off-by-one Stack-based Buffer Overflow in tokenizer_string

Quick assessment

Affected
bacnet-stack bacnet-stack
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

BACnet Protocol Stack是一个适用于多种平台的，用于提供BACnet应用层、网络层和媒体访问（MAC）层通信服务的库。 BACnet Protocol Stack 1.4.2版本、1.5.0.rc2版本及之前版本存在安全漏洞，该漏洞源于ubasic解释器中存在差一栈缓冲区溢出，可能导致处理超长字符串字面量时崩溃。

CVSS 5.5 · Medium EPSS 0.26% · P16

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution
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I. Basic Information for CVE-2026-21870

Vulnerability Information
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Vulnerability Title
The BACnet Protocol Stack library has an Off-by-one Stack-based Buffer Overflow in tokenizer_string
Source: CVE Program / CVE List V5
Vulnerability Description
BACnet Protocol Stack library provides a BACnet application layer, network layer and media access (MAC) layer communications services. In 1.4.2, 1.5.0.rc2, and earlier, an off-by-one stack-based buffer overflow in the ubasic interpreter causes a crash (SIGABRT) when processing string literals longer than the buffer limit. The tokenizer_string function in src/bacnet/basic/program/ubasic/tokenizer.c incorrectly handles null termination for maximum-length strings. It writes a null byte to dest[40] when the buffer size is only 40 (indices 0-39), triggering a stack overflow.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
Off-by-one错误
Source: CVE Program / CVE List V5
Vulnerability Title
BACnet Protocol Stack 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
BACnet Protocol Stack是一个适用于多种平台的，用于提供BACnet应用层、网络层和媒体访问（MAC）层通信服务的库。 BACnet Protocol Stack 1.4.2版本、1.5.0.rc2版本及之前版本存在安全漏洞，该漏洞源于ubasic解释器中存在差一栈缓冲区溢出，可能导致处理超长字符串字面量时崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
bacnet-stack bacnet-stack <= 1.4.2 -

II. Public POCs for CVE-2026-21870

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III. Intelligence Information for CVE-2026-21870

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Patches & Fixes for CVE-2026-21870 (1)

Same Patch Batch · bacnet-stack · 2026-02-13 · 3 CVEs total

CVE-2026-21878 7.5 HIGH BACnet Stack Improperly Limits Pathnames to a Restricted Directory
CVE-2026-26264 BACnet Stack WriteProperty decoding length underflow leads to OOB read and crash

IV. Related Vulnerabilities

Same product: bacnet-stack
Same vendor: bacnet-stack
Same weakness: CWE-193

V. Comments for CVE-2026-21870

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